If I recall correctly, campers who you successfully invite into your town don't always plot their house the next day after. Sometimes it takes 2-3 days (and you can sometimes stall camper moves ins a few days with plot resetting).
On the other hand, villagers who you successfully invite over from another users town do plot their house the next day after and persist to plot on that day.
So, it would seem as though Julian would have top priority to move - especially if Dotty wasn't planning to move in until a few days later. Of course, if you have 9 villagers already and Julian plots then that specific campsite Dotty has no chance to move in.